The present invention relates to a device for the reduction of noise in a radar receiver. It can be applied especially to radars fitted into automobiles. More generally, it can apply to radars requiring low-cost manufacture while at the same time having high performance characteristics in regard to noise.
There are many types of architectures of radar reception circuits. Heterodyne receivers are known to provide great sensitivity but have a high cost price. This is incompatible with low-cost applications such as for example radars fitted into automobiles. In the latter case, the goal of reduced cost is all the more crucial as it is being planned to equip medium-budget vehicles with radars especially for road traffic regulation and control applications. Radars of this kind for example have the function of detecting the distance between and relative speeds of a carrier vehicle and a vehicle in front of it in order to enable the carrier vehicle to adjust its speed with respect to the preceding vehicle, in particular in order to comply with safety criteria.
The advantage of a homodyne receiver is that it can be produced at low cost especially because of its simplicity. In view of this advantage, plans are being made to use it especially for automobile applications. However, it has low sensitivity. Indeed, the target signal is directly transposed into baseband, namely into the very low frequencies, without particular amplification, and often without any amplification whatsoever. Now, components such as mixers or video frequency amplifiers for example are affected by a high level of colored additive noise whose spectral density varies according to a 1/F.sup.k relationship, with F representing a frequency related to the transmitted carrier wave.
A homodyne receiver is furthermore subjected to other types of noises. These noises may be for example wideband white thermal noise coming from the antenna, the microwave mixer or amplifiers inserted between the antenna and the mixer. They may also be phase and amplitude noises from the wave generator carried by the targets or noises caused by insulation defects in the microwave circuits.